To understand the prior art upon which the present invention seeks to improve, attention is directed to the specification of U.S. Pat. No. 4,542,649, issued to Charbonneau et al (the "649 patent"). Specifically, attention is directed to the "Stem Load Calibration Device" in which a load cell disc is suspended by a plurality of rods above a fixed (or relatively fixed) object. In the case of the 649 patent, the "fixed" object is a valve operator housing. The load disc device of the 649 patent is of a type which measures compressive forces exerted directly on a load bearing surface of the load cell body by a shaft (or shaft extension) moving relative to the "fixed" housing. There are other load measuring mechanisms with varying arrangements of the load bearing surfaces, shaft blocking components and strain gauges which have attempted, with varying degrees of success, to perform the function of the stem load measuring device of the 649 patent.
In spite of the availability of numerous load measuring mechanisms, the need for improvements has been noted. For example, the Stem Load Calibration Device of the 649 patent has found extensive application as part of valve diagnostic equipment utilized to diagnose valve and valve operator conditions within nuclear power plants. When working in a nuclear environment, there exists the desire and need to accomplish tasks as quickly as possible. The 649 patent, Stem Load Calibration Device and other known load measuring mechanisms include a plurality of separate components which are assembled on site at the valve operator; or, in some cases, the load measuring mechanisms include few parts but require some degree of disassembly and reassembly of the valve operator. A second example of an area for improvement is that many prior art load measuring mechanisms offer no protection against overloading of the valve operator. As such, extremely large and potentially damaging forces can be built up within the operator during the diagnostic process.